Electric fan

ABSTRACT

An electric fan is provided, including a labyrinth structure with increased performance of preventing entry of a liquid into a receiving space to receive a stator and a rotor. A clearance is defined between an opposed wall portion of a base and an opposed wall portion of an impeller body, which are opposed to each other in an axial direction of a rotary shaft, to form a labyrinth structure. The opposed wall portion of the base and the opposed wall portions of the impeller body are shaped to form a volume expanding portion within the clearance. The volume expanding portion is constituted from a groove portion for expanding the clearance, having a volume larger than other portions within the clearance.

TECHNICAL FIELD

The present invention relates to an electric fan such as an axial fanand a centrifugal fan, which uses an electric motor as a driving source.

BACKGROUND ART

An electric fan which comprises an impeller and a casing is known. Theimpeller includes a plurality of blades and is configured to rotate byan electric motor. The casing includes a base which defines a receivingspace to receive a stator and a rotor of the electric motor. In such anelectric fan, a liquid such as water may enter into the receiving spacefrom between an impeller body of the impeller and the base. In order tocope with this problem, Japanese Patent No. 3694224 (JP3694224), forexample, proposes that a clearance be defined between a casing and animpeller of a centrifugal fan to form a labyrinth structure for blockingentry of a liquid into a receiving space.

SUMMARY OF THE INVENTION

There is a limit to enhancing waterproof performance of a conventionalstructure for preventing entry of the liquid into the receiving spaceeven if a clearance is provided to form a labyrinth structure asmentioned above.

Further, when the clearance forming the labyrinth structure is defined,dimensional tolerances of the casing and the impeller are reduced. Thus,assembly accuracy of the impeller body and the casing of the electricfan needs to be increased.

An object of the present invention is to provide an electric fan inwhich waterproof performance may be enhanced by using a labyrinthstructure which prevents a liquid from entering into a receiving spaceto receive a stator and a rotor, as compared with conventional electricfans.

Another object of the present invention is to provide an electric fanincluding a labyrinth structure by which waterproof performance may notbe reduced so significantly as in conventional electric fans even ifassembly accuracy of the electric fan is lower than that in conventionalelectric fans.

An electric fan such as an axial fan or a centrifugal fan, improvementof which is aimed at by the present invention, comprises an electricmotor, an impeller, a casing, and one or more bearings. The electricmotor comprises a rotary shaft, a stator including stator magneticpoles, and a rotor including rotor magnetic poles and configured torotate outside the stator, centering on the rotary shaft. The impelleris disposed outside the rotor, and includes an impeller body fixed tothe rotor and including an opposed wall portion, and a plurality ofblades fixed to the impeller body. The casing includes a bearing holderby which the one or more bearings for supporting the rotary shaft areheld, and a base including an opposed wall portion opposed to theopposed wall portion of the impeller body in an axial direction of therotary shaft and extending in a radial direction of the rotary shaft andcombined with the impeller body to define a receiving space to receivethe stator and the rotor. Then, a clearance is defined between theopposed wall portion of the base and the opposed wall portion of theimpeller body to form a labyrinth structure for blocking entry of aliquid into the receiving space from radially outside of the rotaryshaft. In the present invention, the opposed wall portion of the baseand the opposed wall portion of the impeller body are shaped to form oneor more volume expanding portions each having a volume larger than otherportions within the clearance.

In a specific electric fan which is configured by applying the presentinvention to a centrifugal fan, the impeller body of the impellerincludes a fixed portion fixed to the rotor, and a blade support fixedto the fixed portion and extending in the radial direction of the rotaryshaft. Then, the blades are fixed to the blade support of the impellerbody to suck an air from a side on which one axial end of the rotaryshaft of the electric motor is located and discharge the air in theradial direction of the rotary shaft. The casing includes the bearingholder by which the one or more bearings for supporting the rotary shaftare held, and the base extending in the radial direction of the rotaryshaft and combined with the fixed portion to define the receiving spaceto receive the stator and the rotor.

Since the one or more volume expanding portions are formed within theclearance which forms the labyrinth structure in the present invention,the liquid which has entered into the clearance pools in the one or morevolume expanding portions. Then, after the one or more volume expandingportions have been filled with the liquid, the liquid goes furthertoward the receiving space. As a result, a period of time until theliquid enters into the receiving space is longer than that in theconventional structure, thereby enhancing the waterproof performanceaccording to the present invention. Further, by providing the one ormore volume expanding portions, the volume of the entire labyrinthstructure may be increased more than the conventional structure, therebyenhancing the waterproof performance. Accordingly, dimensionaltolerances of the casing and the impeller do not need to be reduced somuch as in conventional structures in order to enhance the waterproofperformance. Even if assembly accuracy of the electric fan is lower thanthose of conventional structures, the waterproof performance is notsignificantly reduced.

The volume expanding portion may be formed in a variety ofconfigurations. If the thickness of the opposed wall portion of theimpeller body as measured in the axial direction is large, for example,a groove portion for expanding the clearance may be formed in theopposed wall portion of the impeller body. The groove portion extends ina direction apart from the base to define a main part of the volumeexpanding portion. Alternatively, when the thickness of the opposed wallportion of the base as measured in the axial direction is large, agroove portion for expanding the clearance may be formed in the opposedwall portion of the base. The groove portion extends in a directionapart from the impeller body to define a main part of the volumeexpanding portion. Thus, the volume expanding portion may appropriatelybe formed according to the specification of an electric fan.

Alternatively, a groove portion for expanding the clearance may beformed in the opposed wall portion of the impeller body, and a grooveportion for expanding the clearance may be formed in the opposed wallportion of the base as well. The groove portion in the opposed wallportion of the impeller body extends in a direction apart from the baseto define a part of the volume expanding portion. The groove portion inthe opposed wall portion of the base extends in a direction apart fromthe impeller body to define the remaining part of the volume expandingportion. In this configuration, even if the thicknesses of the opposedwall portion of the impeller body and the opposed wall portion of thebase as measured in the axial direction are small, the volume expandingportion of a certain size may be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and many of the attendant advantages of thepresent invention will be readily appreciated as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings.

FIG. 1 is a sectional view of an electric fan in a first embodiment ofthe present invention applied to a centrifugal fan.

FIG. 2 is a partially enlarged view of a portion indicated by referencesign M in FIG. 1.

FIG. 3 is a sectional view of an electric fan in a second embodiment ofthe present invention applied to a centrifugal fan.

FIG. 4 is a partially enlarged view of a portion indicated by referencesign M in FIG. 3.

FIG. 5 is a sectional view of an electric fan in a third embodiment ofthe present invention applied to a centrifugal fan.

FIG. 6 is a partially enlarged view of a portion indicated by referencesign M in FIG. 5.

FIG. 7 is a sectional view of an electric fan in a fourth embodiment ofthe present invention applied to a centrifugal fan.

FIG. 8 is a partially enlarged view of a portion indicated by referencesign M in FIG. 7.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below in detailwith reference to the drawings. FIG. 1 is a sectional view of anelectric fan in a first embodiment of the present invention applied to acentrifugal fan. FIG. 2 is a partially enlarged view of a portionindicated by reference sign M in FIG. 1. The electric fan of thisembodiment comprises an electric motor 1, an impeller 3 made of asynthetic resin and configured to be rotated by the electric motor 1,and a casing 5 for partially receiving components of the electric motor1. The electric motor 1 includes a stator 7 and a rotor 11 configured torotate outside the stator 7, centering on a rotary shaft 9. The stator 7is mounted on a bearing holder 43 in which two ball bearings 13 and 15for rotatably supporting the rotary shaft 9 are fitted and held. Thestator 7 comprises a stator core 19 disposed outside this bearing holder43, an insulator 21 made of an insulating resin and fitted with thestator core 19, and stator windings 23 wound around a plurality of poleportions of the stator core 19 through the insulator 21. The statorwindings 23 are each electrically connected to a circuit pattern of acircuit board 27, not shown, through a connecting conductor 25. A drivecircuit is mounted on the circuit board 27 for feeding an excitationcurrent through the stator windings 23.

The rotor 11 comprises a cylindrical boss 29 made of an insulatingmaterial and fixed to the rotary shaft 9, a cup-like member 31 made of amagnetic conductive material and fixed to the rotary shaft 9 through theboss 29, and rotor magnetic poles 33 formed of a plurality of permanentmagnets and fixed to the cup-like member 31. The cup-like member 31includes a bottom wall portion 31 a having in a central portion thereofa through hole through which the boss 29 passes and a cylindricalperipheral wall portion 31 b extending from an outer edge of the bottomwall portion 31 a in an axial direction of the rotary shaft 9. Thepermanent magnets constituting the rotor magnetic poles are bonded to aninner peripheral surface of the peripheral wall portion 31 b of thecup-like member 31 to face a magnetic pole surface of the stator core 19constituting stator magnetic poles of the stator 7.

The impeller 3 includes an impeller body 35 and a plurality of blades37. The impeller body 35 and the blades 37 are unitarily formed of asynthetic resin. The impeller body 35 includes a fixed portion 39 fixedto an outside of the cup-like member 31 of the rotor 11 of the electricmotor 1, a blade support 41 fixed to the fixed portion 39 and extendinga radial direction of the rotary shaft. Each blade 37 has a first endand a second end. The first ends of the blades 37 are fixed to the bladesupport 41, and the second ends of the blades 37 are fixed to an annularshroud 42. Each blade 37 is shaped to suck an air from a side on whichone axial end of the rotary shaft 9 is located, namely, from a side ofthe annular shroud 42 and to discharge the air in the radial directionof the rotary shaft 9. The fixed portion 39 has a cup shape joined tothe cup-like member 31. The blade support 41 includes a truncatedconical cylindrical portion 41 a and an annular blade mounting portion41 b. One end of the truncated conical cylindrical portion 41 a isunitarily formed with the cup-like member 31, and has a diameter whichincreases toward the other axial end of the rotary shaft 9. The annularblade mounting portion 41 b is unitarily formed with the other end ofthe truncated conical cylindrical portion 41 a and extends in the radialdirection of the rotary shaft 9. The blades 37 are mounted on theannular blade mounting portion 41 b.

The casing 5 for partially receiving the components of the electricmotor 1 unitarily includes a base 45 and the bearing holder 43 by whichthe bearings 13 and 15 are held. The base 45 extends in the radialdirection of the rotary shaft 9, and is combined with the fixed portion39 of the impeller body 35 to define a receiving space 47 to receive thestator 7 and the rotor 1.

As shown in FIG. 2, an annular projecting portion 45 b projecting towardthe impeller body 35 is formed on an opposed wall portion 45 a of thebase 45 opposed to the impeller body 35. An annular concave portion 35 bis formed in an opposed wall portion 35 a of the impeller body 35. Theannular projecting portion 45 b is inserted into the annular concaveportion 35 b with a gap interposed between the annular projectingportion 45 b and the annular concave port on 35 b. In such aconfiguration, a clearance 49 is defined between the base 45 and theimpeller body 35 to form a labyrinth structure. The clearance 49 whichforms the labyrinth structure serves to block entry of a liquid into thereceiving space 47, which receives the stator 7 and the rotor 11, fromradially outside of the rotary shaft 9. In this embodiment, theclearance 49 forming the labyrinth structure includes a groove portion49 a for expanding the clearance. The groove portion 49 a is formed inthe opposed wall portion 35 a of the impeller body 35 to communicatewith the clearance 49. The groove portion 49 a extends in a directionapart from the base 45. In this embodiment, the clearance 49 includes acrank portion bending to partially face the leading end of theprojecting port ion 45 b that is formed in a portion 35 c of theimpeller body 35 located more radially inward of the rotary shaft 9 thanthe groove portion 49 a. The groove portion 49 a is provided within theclearance 49 to define a main part of a volume expanding portion 50having a volume larger than other portions within the clearance 49. Inother words, the opposed wall portion 45 a of the base 45 and theopposed wall portion 35 a of the impeller body 35 are opposed to eachother in the axial direction to define the clearance 49 and are shapedto form the volume expanding portion 50.

In the electric fan in this embodiment, the volume expanding portion 50is formed within the clearance 49 which forms the labyrinth structure.Thus, the liquid, which has entered into the clearance 49, pools withinthe volume expanding portion 50. As a result, entry of the liquid intothe receiving space 47 may be blocked until the liquid, which has pooledwithin the volume expanding portion 50, goes further toward thereceiving space 47. Accordingly, in this embodiment, a period of timefor entry of the liquid into the receiving space may be prolonged, ascompared with conventional configurations. A maximum waterproof effectmay be exerted in the centrifugal fan of this embodiment especially whenthe electric fan is used with the casing located in an upper positionand the impeller located in a lower position, which is a reversepositional relationship of FIG. 1.

FIG. 3 is a sectional view of an electric fan in a second embodiment ofthe present invention applied to a centrifugal fan. FIG. 4 is apartially enlarged view of a portion indicated by reference sign M shownin FIG. 3. Though dimensions and shapes of respective members of theelectric fan in this embodiment are different from those of thecorresponding members in the electric fan shown in FIGS. 1 and 2, theelectric fan of this embodiment has basically the same structure as theelectric fan shown in FIGS. 1 and 2 except a cup-like member, a base ofa casing, and an impeller body. Therefore, reference numerals calculatedby adding 100 to the reference numerals in FIGS. 1 and 2 are assigned tomembers in FIGS. 3 and 4 which have basically the same structures asthose in FIGS. 1 and 2. Descriptions of the members in FIGS. 3 and 4will thereby be omitted.

As shown in FIG. 3, the electric fan in this embodiment does not includethe cup-like member fixed to the rotary shaft. Rotor magnetic poles 133formed of a plurality of permanent magnets are fixed to a cylindricalmember 131 made of a magnetic conductive material.

In the electric fan of this embodiment, two annular projecting portions145 c and 145 d projecting toward an impeller body 135 are formed on anopposed wall portion 745 a of a base 145 opposed to the impeller body135, as shown in FIG. 4. Further, three annular projecting portions 135d to 135 f projecting toward the base 145 are formed on an opposed wallportion 135 a of the impeller body 135. The projecting portion 145 c ofthe base 145 is inserted into an annular concave portion between theprojecting portions 135 d and 135 e of the impeller body 135 with a gapinterposed between an inner surface of the concave portion and theprojecting portion 145 c. The projecting portions 135 e and 135 f of theimpeller body 135 are inserted into an annular concave portion betweenthe projecting portions 145 c and 145 d of the base 145 with a gapinterposed between the projecting portions 135 e and 135 f and an innersurface of the annular concave portion. In such a configuration, aclearance 149 is defined between the base 145 and the impeller body 135to form a labyrinth structure. A first groove portion 149 a forexpanding the clearance and a second groove portion 149 b for expandingthe clearance are included in the clearance 149. The first grooveportion 149 a is formed in the opposed wall portion 135 a of theimpeller body 135 to extend in a direction apart from the base 145. Thesecond groove portion 149 b is formed in the opposed wall port ion 145 aof the base 145 to extend in a direction apart from the impeller body135. The first groove portion 149 a defines a part of a volume expandingportion 150 having a volume larger than other portions within theclearance 149. The second groove portion 149 b defines the remainingpart of the volume expanding portion 150 having the volume larger thanthe other portions within the clearance 149. In other words, the opposedwall portion 145 a of the base 145 and the opposed wall portion 135 a ofthe impeller body 135 are opposed to each other in an axial direction ofthe rotary shaft to define the clearance 149 and are shaped to form thevolume expanding portion 150 within the clearance 149.

According to the electric fan of this embodiment, even if dimensions ofboth of the opposed wall portion 135 a of the impeller body 135 and theopposed wall portion 145 a of the base 145 as measured in the axialdirection are small, the volume expanding portion 150 of a certain sizemay be formed by the first groove portion 149 a and the second grooveportion 149 b. Accordingly, this contributes to overall downsizing ofthe electric fan in the axial direction. Further, according to theelectric fan of this embodiment, regardless of how to dispose theelectric fan as viewed in the axial direction, specifically, regardlessof which one of the impeller and the casing is disposed higher than theother of them as viewed in the axial direction, entry of a liquid into areceiving space 147 may be prevented until one of the first grooveportion 149 a and the second groove portion 149 b is filled with theliquid.

FIG. 5 is a sectional view of an electric fan in a third embodiment ofthe present invention applied to a centrifugal fan. FIG. 6 is apartially enlarged view of a portion indicated by reference sign M inFIG. 5. Though dimensions and shapes of respective members are differentfrom those of the corresponding members in FIGS. 1 and 2, the electricfan of this embodiment has basically the same structure as the electricfan shown in FIGS. 1 and 2 except the configuration of a groove portionfor expanding a clearance. Therefore, reference numerals calculated byadding 200 to the reference numerals in FIGS. 1 and 2 are assigned tomembers in FIGS. 5 and 6 which have basically the same structures asthose in FIGS. 1 and 2. Descriptions of the members in FIGS. 5 and 6will thereby be omitted.

In the electric fan of the first embodiment shown in FIGS. 1 and 2, thewall portion 35 c of the impeller body 35 located radially inside of theannular groove portion 49 a constituting the volume expanding portion 50partially faces the projecting portion 45 b. In the electric fan of thisembodiment, a wall portion 235 c of an impeller body 235 locatedradially inside of a groove portion 249 a for expanding a clearance doesnot face the leading end of a projecting portion 245 b. Thus, thedimension of an opening portion of the groove portion 249 a in a radialdirection of a rotary shaft 209 is larger than that in the electric fanof the first embodiment. However, the groove portion 249 a has a smallerlength or depth in an axial direction than in the electric fan in thefirst embodiment. As a result, a cross-sectional shape of the grooveportion 249 a which constitutes a main part of a volume expandingportion 250 is substantially a triangle, as clearly known from FIG. 6. Amaximum waterproof effect may be exerted in the electric fan of thisembodiment when the electric fan is used with the casing located in anupper position and the impeller located in a lower position, which is areverse positional relationship of FIG. 5 as in the electric fan of theembodiment shown in FIG. 1.

FIG. 7 is a sectional view of an electric fan in a fourth embodiment ofthe present invention applied to a centrifugal fan. FIG. 8 is apartially enlarged view of a portion indicated by reference sign M inFIG. 7. Though dimensions and shapes of respective members are differentfrom those of the corresponding members in FIGS. 1 and 2, the electricfan of this embodiment has basically the same structure as the electricfan shown in FIGS. 1 and 2 except a base of a casing and an impellerbody. Therefore, reference numerals calculated by adding 300 to thereference numerals in FIGS. 1 and 2 are assigned to members in FIGS. 7and 8 which have basically the same structures as those in FIGS. 1 and2. Descriptions of the members in FIGS. 7 and 8 will thereby be omitted.

As shown in FIG. 8, two annular projecting portions 345 e and 345 fprojecting toward an impeller body 335 are formed on an opposed wallportion 345 a of a base 345 of the electric fan, the opposed wallportion 345 a being opposed to the impeller body 335. Two annularprojecting portions 335 g and 335 h projecting toward the base 345 areformed on an opposed wall portion 335 a of the impeller body 335. Theprojecting portion 345 e of the base 345 is inserted into a concaveportion formed between the projecting portions 335 g and 335 h of theimpeller body 335 with a gap interposed between an inner surface of theconcave portion and the projecting portion 345 e. The annular projectingportion 335 h provided on the impeller body 335 is inserted into aconcave portion 345 g formed between the annular projecting portions 345e and 345 f provided on the base 345, with a gap interposed between aninner surface of the concave portion 345 g and the annular projectingportion 335 h. In such a configuration, a clearance 349 is definedbetween the base 345 and the impeller body 335 to form a labyrinthstructure. A groove portion 349 a for expanding the clearance isincluded in the clearance 349. The groove portion 349 a is formed in theopposed wall portion 345 a of the base 345 to extend in a directionapart from the impeller body 335. The groove portion 349 a defines amain part of a volume expanding portion 350 having a volume larger thanother portions within the clearance 349. In other words, the opposedwall portion 345 a of the base 345 and the opposed wall portion 335 a ofthe impeller body 335 are opposed to each other in an axial direction todefine the clearance 349 and are shaped to form the volume expandingportion 350. A maximum waterproof effect may be exerted in thecentrifugal fan of this embodiment when the electric fan is used withthe base 345 located in a lower position and the impeller body 335located in an upper position as shown on the page of FIG. 7.

Each of the above-mentioned embodiments shows an application example ofthe present invention suited to the centrifugal fan. The presentinvention may also be applied to other types of electric fans such as anaxial fan and an oblique flow fan.

According to the present invention, the volume expanding portion isformed with in the clearance which forms the labyrinth structure. Thus,the liquid that has entered into the clearance pools in the volumeexpanding portion. A period of time until the liquid enters into thereceiving space may be prolonged, as compared with conventionalstructures, thereby enhancing waterproof performance. Further, thevolume of the entire labyrinth structure may be increased more than inconventional structures by forming the volume expanding portion, therebyenhancing the waterproof performance as well. Accordingly, dimensionaltolerances of the casing and the impeller do not need to be reduced somuch as in the conventional structures. Even if assembly accuracy of theelectric fan is lower as compared with the conventional structures, thewaterproof performance may not be significantly reduced.

While the preferred embodiments of the invention have been describedwith a certain degree of particularity with reference to the drawings,obvious modifications and variations are possible in light of the aboveteachings. It is therefore to be understood that within the scope of theappended claims, the invention may be practiced otherwise than asspecifically described.

1. An electric fan comprising: an electric motor including: a rotaryshaft; a stator including stator magnetic poles; and a rotor includingrotor magnetic poles and configured to rotate outside the stator,centering on the rotary shaft; an impeller disposed outside the rotor,the impeller including: an impeller body fixed to the rotor andincluding an opposed wall portion; and a plurality of blades fixed tothe impeller body; one or more bearings for supporting the rotary shaft;and a casing including; a bearing holder by which the one or morebearings are held; and a base including an opposed wall portion opposedto the opposed wall portion of the impeller body in an axial directionof the rotary shaft and extending in a radial direction of the rotaryshaft and combined with the impeller body to define a receiving space toreceive the stator and the rotor, wherein a clearance is defined betweenthe opposed wall portion of the base and the opposed wall portion of theimpeller body to form a labyrinth structure for blocking entry of aliquid into the receiving space from radially outside of the rotaryshaft; and the opposed wall portion of the base and the opposed wallportion of the impeller body are shaped to form one or more volumeexpanding portions each having a volume larger than other portionswithin the clearance.
 2. The electric fan according to claim 1, whereinthe impeller body includes: a fixed portion fixed to the rotor; and ablade support fixed to the fixed portion and extending in the radialdirection of the rotary shaft; the blades are fixed to the blade supportof the impeller body to suck an air from a side on which one axial endof the rotary shaft of the electric motor is located and discharge theair in the radial direction of the rotary shaft; and the base iscombined with the fixed portion.
 3. The electric fan according to claim1, wherein a groove portion for expanding the clearance is formed in theopposed wall portion of the impeller body, the groove portion extendingin a direction apart from the base to define a main part of the volumeexpanding portion.
 4. The electric fan according to claim 1, wherein agroove portion for expanding the clearance is formed in the opposed wallportion of the base, the groove portion extending in a direction apartfrom the impeller body to define a main part of the volume expandingportion.
 5. The electric fan according to claim 1, wherein a grooveportion for expanding the clearance is formed in the opposed wallportion of the impeller body, the groove portion extending in adirection apart from the base to define a part of the volume expandingportion; and a groove portion for expanding the clearance is formed inthe opposed wall portion of the base, the groove portion extending in adirection apart from the impeller body to define the remaining part ofthe volume expanding portion.